Solar concentrators are used to collect energy emitted by the sun in the form of radiation. Known solar concentrators are shaped so as to direct sunlight incident on a large area spanned by the solar concentrator into a much smaller target area occupied by a device which converts the sun's radiation in the form of light and/or heat into usable energy. Generally the configurations of solar concentrators include a combination of reflectors, lenses, and radiation diffusers. Typical known solar concentrators often utilize a large single or compound reflector for concentrating sunlight incident upon a relatively large area into a smaller target area at which location further reflectors, lenses and/or diffusers are used to further focus and/or diffuse the incident radiation prior to its falling incident upon the target device for conversion into usable energy.
One known base shape that is often used for solar concentrators is the parabola. A two-dimensional parabola has the property that, at any point on the parabola, the angle between a line passing through the point parallel with the axis of symmetry of the parabola, and the normal of the curve at that point on the parabola, is the same as the angle between the normal and a line passing through the point and what is known as the focus of the parabola. Consequently, parallel rays from infinity are focused into a single point or a relatively small area located at the focus.
Two widely used types of parabolic reflectors, having a three-dimensional form based on the parabola, are the parabolic trough and the parabaloid or parabolic dish reflector.
A parabolic trough is a trough shaped reflector which has, in any plane perpendicular to its length, a two-dimensional profile in the shape of a parabola, and hence has a three-dimensional shape of that parabola extruded along the length of the trough. This kind of reflector has a focal line running the length of the trough and passing through the foci of the parabolas in the planes perpendicular to its length.
A parabolic dish reflector is a parabaloid shaped reflector which has, in any plane parallel with and intersecting the reflector's axis of rotational symmetry, a two-dimensional profile in the shape of a parabola, and hence has a three-dimensional shape of that parabola rotated about its axis of symmetry. This kind of reflector has a focal point located along the axis of symmetry and at the foci of all the rotationally symmetric parabolas in the planes parallel with and intersecting the axis.
FIG. 1 is a two-dimensional cross-sectional view of a known parabolic concentrator 100 which view is illustrative of both a parabolic trough and a parabolic dish reflector. For simplicity the parabola of the two-dimensional profile of the parabolic reflector of the parabolic concentrator 100 is simply referred to as the parabola 110. Incoming radiation 105i from infinity or the sun which is parallel to the axis of symmetry 102 of the parabola 110 is reflected by the parabola 110 as reflected radiation 105r, which converges at focus 103.
Known systems which collect solar radiation and convert it into thermal energy, typically use a reservoir or conduit such as a pipe containing a liquid which is heated up by the radiation focused by the parabola 110, the thermal energy of which is used ultimately for the generation of electrical energy. FIG. 1 depicts a cross-section of a pipe 122 which is for conducting fluid to be heated near the focus 103 of the parabola 110. The pipe 122 is located at a distance 101b from the parabola 110 which is substantially at the focus 103 of the parabola 110 such that most or all of the reflected radiation 105r of the parabola 110 is incident upon the surface of the pipe 122. The materials used for the pipe 122, or other reservoir or conduit, at least in the region substantially at the focus 103 of the parabola 110, are such that they are capable of withstanding the intensity of the reflected radiation 105r focused by the parabolic reflector 100 and are ideal for converting the reflected radiation 105r into thermal energy and transferring that energy in the form of heat to the fluid passing therethrough.
Known systems which collect solar energy by converting light directly into electricity typically utilize photovoltaic (PV) cells arranged in a PV panel or unit to collect the light focused by the parabola 110 and convert it into electrical current. Typically, PV units are of finite dimensions, having a finite area spanned by a number of PV cells, and have maximal efficiency when the radiation incident upon the photovoltaic cells of the PV unit have the same intensity i.e. when the incident radiation upon the active area of the PV unit is homogeneous. In general a PV unit's efficiency is limited by the lowest intensities incident upon its radiation collecting surface, and consequently, localized shadows or minima in the incident radiation are a concern whereas localized bright areas or maxima are generally not. Additionally, there are limits to the intensity of the radiation to which any portion of a PV unit may be subjected without it malfunctioning or undergoing permanent irreparable damage. Hence, a PV unit is typically positioned either between the focus 103 and the parabola 110 such as a PV unit 120a at a distance 101a from the parabola 110, or at a distance beyond the focus 103 from the parabola 110, such as a PV unit 120b at a distance 101c from the parabola 110. Due to the finite area of the PV unit, not all of the incident radiation 105i near the axis of symmetry 102 will be incident upon the parabola 110. Specifically, a shadow is cast by the PV unit 120a, 120b which is reflected as a shadow 108 within the reflected radiation 105r. 
In some known systems utilizing PV units, a radiation diffuser in the form of a substantially transparent plate or lens (not shown for clarity) is positioned so as to intercept and diffuse the radiation reflected by the parabola 110 prior to its falling incident upon the photovoltaic cells of the PV unit 120a, 120b. Although this technique improves homogeneity of the intensity of the radiation incident upon the PV unit 120a, 120b, efficiency is sacrificed due to the energy lost in the form of the radiation reflected or refracted away from the PV unit 120a, 120b by the plate or lens and/or the radiation absorbed by the plate or lens and converted into heat at the plate or lens which is lost to the surrounding environment. As is discussed hereinbelow, the smaller the proportion of the reflected radiation which is diffused with use of a diffuser, the higher the efficiency of the parabolic concentrator 100.
The foregoing applies equally to known parabolic concentrators of both the parabolic trough and parabolic dish types, the difference between them being only that the parabolic dish is rotationally symmetric about a single axis and the parabolic trough is bilaterally symmetric in a plane passing through the axes of the parabolas of the trough.